How to Export to pdf with index limited to level N Headings?

I have an annoying problem, I’ve created a document with a ToC and configured it to evaluate up to level 3 Headings. works great. In the document i have some level 4 headings bacause i may want to include them in ToC in the future. The problem is that when i export to PDF the index is listing ALL headings. I need to limit this to level 3